A logic analyzer is an electronic instrument used to detect, analyze and display digital voltage signals. Typically, a digital voltage signal conveys binary information, that is, the signal is either logic "high" or logic "low." For instance, according to one convention, if the signal voltage is above a given threshold value it is "high" whereas if it is below the threshold value it is "low." (In conventional binary logic, "high" represents a "1" and "low" represents a "0".) Since the signal carries binary information, that is, 1's and 0's, it is the signal's transition above or below the threshold value, rather than its absolute value, that is important.
Like an oscilloscope, the logic analyzer typically displays a signal's waveform as a function of voltage-versus-time with voltage amplitude displayed along a vertical axis and time displayed along a horizontal axis. Unlike an oscilloscope, however, the logic analyzer typically does not display high vertical (that is, voltage) resolution. Rather, for a given signal the logic analyzer waveform will resemble a square-wave and therefore be either "high" or "low." In fact, since the logic analyzer's primary purpose is to display a signal's transitions from 1's to 0's, that is, from logic "high" to logic "low", the square-wave waveform is both adequate and ideal.
Typically, the logic analyzer displays the digital waveforms of many individual signals at once, such as the signals on the multiple lines of a data-bus or an address-bus. The typical logic analyzer can show sixteen digital waveforms at once. Thus, on such an analyzer the signals on the sixteen lines of a 16-bit address bus would be shown as sixteen individual square-wave waveforms positioned from the top to the bottom of the display screen. The user of the logic analyzer can then view the sixteen waveforms simultaneously in a single display.
Typically, the viewer is most interested in comparing the transitions from high to low of numerous waveforms, such as a comparison of the transitions on certain address lines of a microprocessor with the transitions on certain control lines. Unfortunately, the most important information contained in such a display may be difficult to discern, particularly given that the screen may be updated at the rate of 1-to-20 times per second.